Driving mechanism for electronically controlled timepiece

ABSTRACT

A ratchet wheel in the driving mechanism of a timepiece, having pointed teeth alternately engageable by a pair of dogs on opposite ends of an electromagnetically impelled balance lever, coacts with a retaining pawl in the form of a bar or reed swingable about a fulcrum on a line perpendicular to the trailing flank of a tooth engaged by a transverse end face of the pawl. Upon a stepping of the ratchet wheel by the balance lever, the tooth immediately following the one heretofore engaged by the pawl strikes a side face thereof with sufficient force to drive the end face of the pawl out of the orbit of the ratchet teeth, against a magnetic or elastic biasing force, so that this following tooth can move into the engagement position without further contact with the pawl until the latter returns to its blocking position.

United States Patent Dome [ 1 May 30, 1972 [72] Inventor: PetervDome, 1249 Athenaz, Geneva, Switzerland [73} Assignee: Societe Suisse Pour Llndustrie Horlogere S.A., Geneva, Switzerland [22] Filed: Nov. 18, 1970 [21] Appl.No.: 90,573

FREQUENCY PULSE OICILLATDE DIV/DEE SHAPE/3 FOREIGN PATENTS OR APPLICATIONS 343,912 6/1960 Switzerland ..58/28D 897,082 S/l962 Great Britain ..58/28D Primary ExaminerRichard B. Wilkinson Assistant Examiner-Edith Cv Simmons Attorney-Karl F. Ross 57 ABSTRACT A ratchet wheel in the driving mechanism of a timepiece. having pointed teeth alternately engageable by a pair of dogs on opposite ends of an electromagnetically impelled balance lever, coacts with a retaining pawl in the form of a bar or reed swingable about a fulcrum on a line perpendicular to the trailing flank of a tooth engaged by a transverse end face of the pawl. Upon a stepping of the ratchet wheel by the balance lever, the tooth immediately following the one heretofore engaged by the pawl strikes a side face thereof with sufficient force to drive the end face of the pawl out of the orbit of the ratchet teeth, against a magnetic or elastic biasing force, so that this following tooth can move into the engagement position without further contact with the pawl until the latter returns to its blocking position.

10 Claims, 4 Drawing Figures Patented May 30, 1972 3,665,697

FREQUENCY PULSE OJCILLAIUE DIV/DEE SHAPEB FIG. 2

Peter Db'me Inventor.

Attorney DRIVING MECHANISM FOR ELECTRONICALLY CONTROLLED TIMEPIECE My present invention relates to a driving mechanism as used in timepieces with an electronically stepped clockwork.

In my commonly owned application, Ser. No. 838,422, filed 2 July 1969, now US. Pat. No. 3,604,201, there has been disclosed a timepiece with an electronic clockwork wherein a unidirectionally rotatable ratchet wheel, forming part of a gear train for driving the hands of the watch or clock, is alternately engaged by a pair of dogs or beaks at opposite ends of a balance lever which is rocked by electronically generated impulses occurring at a fixed cadence. The teeth of the ratchet wheel are pointed so as to form beveled edges or flanks which are camrnable by the dogs in the direction of rotation so that the wheel advances by one tooth division during each rocking cycle.

Such a system, which positively locks the ratchet wheel at the end of each swing of the balance lever, is highly useful since it minimizes the possibility of an untimely advance of the wheel in response to external shocks. Nevertheless, during part of each swing the dogs of the lever are separated sufficiently from the ratchet teeth to enable at least a limited rotation of the wheel by impact or vibration from outside the system so that oscillation of the lever may be temporarily blocked by the resulting disalignment with consequent skipping of one or more stepping cycles.

The primary object of my present invention, therefore, is to provide latch means in a clockwork of this general type for positively immobilizing the ratchet wheel during those phases of operation when its teeth are disengaged from the associated stepping mechanism.

A more specific object is to provide intermittently effective latch means for the purpose set forth whose tooth-engaging element is automatically withdrawable from the orbit of the ratchet teeth without the assistance of an additional source of energy-(other than the pulse generator driving the balance lever), such withdrawal being sufficiently rapid and sustained to minimize the time of contact between the latching element and the moving ratchet teeth and to reduce the wear upon these teeth inherent in such contact.

It is'also an object of my invention to provide a highly compact latching device for the aforestated purpose whose presence does not substantially encumber the moving parts of the clockwork and does not require the expenditure of substantial additional electrical energy.

These objects are realized, in accordance with my present invention, by the provision of an elongate pawl member which is engageable with the pointed ratchet teeth at a location offset from the stepping mechanism and which has an end face positioned to contact the trailing flank of an aligned ratchet tooth, i.e., the rear flank of that tooth as viewed in the direction of rotation, this pawl member being swingable about a fulcrum lying on a line perpendicular to that rear flank when the pawl member is in a contact position in which its end face obliquely intersects the orbit of the teeth. A side face of the pawl member, adjoining the aforementioned end face, then spacedly confronts the tip of an oncoming tooth immediately following the aligned tooth whereby, upon the next advance, this oncoming tooth strikes that side face and thrusts the pawl member out of its orbit against a biasing force which urges the pawl member into its contact position. For effective operation, the mass of the pawl member and the biasing force acting thereon should be so related that, in response to an incremental rotary motion imparted to the ratchet wheel by the stepping mechanism, the pawl member is deflected to an extent and for a time sufficient to clear the tip of the oncoming tooth during the remainder of the stepping movement, i.e., while the latter tooth takes the place of its predecessor.

Advantageously, the line running through the fulcrum of the pawl member at right angles to the rear flank of the aligned tooth in the quiescent position of the system terminates substantially at the tip of that tooth, with the end face of the pawl member narrow enough so as not to intercept the tip of the next tooth upon its return swing.

The pawl member may be biased by a spring force, electromagnetically, or in any other suitable manner and may coact with a stop blocking its swing past the contact position under the urging of its biasing force. With magnetic biasing, this member may conveniently be an at least partly ferromagnetic bar in the field of an associated magnet. A resilient biasing force may be inherent in the pawl member itself, as where the latter is designed as a reed clamped at an end remote from the ratchet wheel, or may be supplied by a separate loading spring. A reed-type pawl, ifused, advantageously is weighted at its free end by an enlarged head provided with the aforedescribed end and side faces; such a block may consist of a crystal, e.g., a ruby, of the type referred to as a jewel in the watchmaking art.

The above and other features of my invention will be described in detail hereinafter with reference to the accompanying drawing in which:

FIG. 1 is a somewhat diagrammatic plan view of an electromechanical clockwork incorporating a driving mechanism according to my invention;

FIG. 2 is a cross-sectional detail view taken on the line Il II of FIG. 1;

FIG. 3 is an explanatory diagram showing parts of the mechanism of FIG. 1 on a larger scale; and

FIG. 4 is a diagrammatic view similar to FIG. 3, illustrating a modification.

FIG. 1 shows major parts of a clockwork of the type disclosed in my above-identified application, Ser. No. 838,422, now US. Pat. No. 3,604,201, including an oscillator OS working into a frequency divider D whose output is delivered to a pulse shaper ER generating a train of stepping pulses of properly calibrated frequency. These stepping pulses appear on an output lead of unit ER integral with two parallel spiral springs 7 (only one shown) which bracket a balance lever l and tend to swing it counterclockwise, i.e., in a sense opposite that of arrow F, about the axis of a shaft 2 transversing the center of that lever. The two ends of lever I carry respective dogs 1a, lb with beveled edges facing in the same direction, these dogs being alternately swingable toward the axis of a ratchet wheel S which may be directly or otherwise positively connected with the seconds hand 21 of the timepiece controlled by the illustrated system. The hour and minute hands 22, 23 are also driven from ratchet wheel S, in the conventional manner, by a gear train diagrammatically illustrated at 20. If the output frequency of stage ER is 1 Hz, wheel S should have 60 teeth so that hand 21 may perform one revolution per minute if its coupling with wheel S has a transmission ratio of 1:1.

An arm 9 rigid with lever 1 is swingable between two fixed stops l3 and 14, being urged against stop 14 by the coil springs 7. The two springs are mutually insulated in a manner not further illustrated and are included in the energizing circuit of a coil 10 movably mounted between two permanent horseshoe magnets 11a, 11b so that its turns intersect the lines of force emanating from each of these magnets. The inner end of the spring 7 visible in the drawing, aside from being anchored to the lever 1, is also mechanically and galvanically connected to a terminal of coil 10 whose other terminal is similarly secured to the companion spring, the clamped outer end of the latter spring being grounded or otherwise returned to the second output terminal of pulse generator ER. With the coil 10 carried on another extension of lever 1 so as to be movable therewith as a unit, its energization by a pulse of predetermined (e.g., positive) polarity from stage ER creates a force which displaces it into its alternate position, i.e., toward magnet lla, so that lever l rocks in a clockwise sense (arrow F) until the arm 9 abuts its alternate stop 13.

The teeth of ratchet wheel S are pointed and have beveled rear flanks s (FIGS. 3 and 4) coacting with the complementarily beveled ends of dogs la, lb whereby each reciprocation of balance lever 1 steps the ratchet wheel S in a counterclockwise sense (arrow F,,) by one tooth division. After each advance by a full step upon a reciprocating swing of the lever, its dog lb positively engages in the gap between two adjoining teeth as illustrated in FIG. 1. As noted in my prior application, stage ER may include a differentiation circuit to generate paired pulses of opposite polarity, the second (e.g., negative) pulse of each pair initiating an early return swing of lever I to withdraw its dog In from the ratchet wheel S before the next tooth hits that dog so that the momentum imparted to the wheel is not wastefully dissipated. The angle included by the coacting beveled faces of dog In and the engaged tooth with the radius of wheel .a' through the point of engagement advantageously is about 45 for optimum energy transfer, as likewise pointed out in the earlier application.

Spaced from the aforedescribed stepping mechanism along the periphery of ratchet wheel S is a latching device or detent comprising a fiat bar 100 of magnetizable material which is pivoted on a fixed pin 101 and whose end'100A intermittently engages the teeth of wheel S, two of which have been designated d and d,. The opposite end 1008 of bar 100 moves between two pole pieces 103, 103A lying on opposite sides of a permanent magnet 102 as best seen in FIG. 2. A fixed support 105 for magnet 102 and its pole pieces 103, 103A carries an adjustable abutment 104 held in position thereon by a screw 106 and normally bearing upon a side face of bar 100, thereby limiting the counterclockwise swing of the bar about pin 101 in response to the magnetic biasing force. The arrested position of the bar can be very precisely adjusted upon loosening of screw 106 and a displacement of abutment 104.

In this arrested position, the transverse face f of bar 100 at its end 100A is in actual or potential contact with the rear flank s, of a tooth d aligned therewith, as more clearly illustrated in FIG. 3. This end face f is perpendicular to a radius r which intersects it in the immediate vicinity of the tip t, of the aligned tooth 41,. The corresponding tip t of the next-following tooth d spacedly confronts a lateral face of bar 100 so that, during the subsequent advance of the ratchet wheel in its permitted direction of rotation (counterclockwise in FIG. 3), the tip I strikes the bar 100 at a point P representing the intersection of this side face with the orbit of the tips of the ratchet teeth. The resulting impact, occurring after the face S of tooth d has become well separated from bar 100, thrusts the bar out of the orbit a so that the tooth a may then move into the erstwhile position of tooth d, without further contact with the bar. 7

After a period determined by such parameters as the initial striking force of tooth d, the moment of inertia of bar 100 and the field strength of magnet 102, the magnetic force restores the bar to its operative position illustrated in FIG. 1; it is now aligned with tooth d,, the ratchet wheel S having come to rest in its new angular position.

In FIG. 4 I have shown a modified detent with a pawl member in the form of a reed 108 clamped in a fixed support 109 which establishes a virtual fulcrum for the reed, this reed being swingable within a range xx and carrying at its free end a block 107 having a side facel07a and an end face 107b, the latter coacting with the rear flanks of the ratchet teeth aligned therewith essentially as heretofore described with reference to FIGS. 1-3.

I shall now explain the mathematical relationships between the various system parameters that must-be observed, in the arrangements of FIGS. 3 and 4, to bring about the desired mode of operation.

Let

1;, denote the radius of orbit a centered on axis 0 (FIG. 3),

5 be the angular distance between point P and tip 1,, i.e., the increment of rotation which tooth d undergoes from the moment of contact with pawl 100 to arrival in its rest position,

r represent the radius of point P as measured from the fulcrum 0 of the pawl,

#1 be the minimum swing angle of pawl 100, i.e., the are over which the point Q of deepest penetration must pass in order to clear the orbit 0 (shown to occur substantially in a position in which that point comes to lie on a line coinciding with the normal position of radius r), and

7 identify the angle between radii r and r.

Let, further,

Hi be the angular velocity imparted to wheel S by the striker 1, 1a,

6 be the angular velocity of the wheel as reduced by the impact of tooth d upon pawl 100,

O be the moment of inertia of the wheel 8 and of the associated gear train 20 and hands 21 23 with reference to the axis 0,

0,, be the moment of inertia of the pawl 100,

k be a fractional coefficient, ranging between 0 and I, which may be referred to as the bounce factor and which is given by the ratio of the velocities of a given object (here the pawl after and before rebounding from a fixed obstacle (here the tooth d, considered stationary at the moment of impact), its magnitude depending upon the materials of the object and the obstacle, I

w be the angular velocity of pawl 100 after impact, and

A be the velocity ratio iri /m which in the present case is close to unity since 0 6 With 3 denoting the angle included between the side face of pawl 100 and the tangent to orbit a in point P, and with a B 7 representing the angle between the same tangent and the radius r it can be shown that ml il 8 Hi Sin S e C08 7 V. r cos y If t,, is the duration of the clockwise swing of pawl 100 (against the action of its magnetic biasing force) under the impact of tooth d, and if t is the time required for tooth d to move into the position of tooth d the first condition to be satisfied in order to prevent interference of pawl- 100 with the motion of wheel S is t zt which leads to the relationship I i z E 8 M mi;

(for )t 1) where M is the restoring torque exerted upon pawl 100 by magnet 102. Furthermore, if (11,, is the total swing angle of pawl 100 from its rest position illustrated in FIG. 3, it can be shown that the second condition to be satisfied for proper performance, i.e.,

Il a #2! requires that e '2 A 5 e 2Me P7 g V In the limiting case where the two terms of expression (3) are equal, the combination of relationships (3) and (5) yields ru /m Zdrddm. For the system of FIG. 4, relationship (4) is replaced by where x is the swing amplitude and p represents half the breadth of head 107 (Le, a distance slightly exceeding the depth of penetration of the head 107 into the orbit of wheel S). Inequality (2) calls for f s y/ 4 (8) where f, the natural frequency of the weighted reed 108, is given by the expression E ab 1 108 upon being If the distance of head 107 from its virtual fulcrum is large, we may assume that a B and 0 whence, given the condition i\ =1 as assumed above, we may derive from Equation l) and inequalities (8) and 10) the relationship V '=w 'r =(l+k)sinB.w '.r (11) For the preferred case of B 45, and with k 0.8 by way of example, the foregoing inequalities yield w 1.25 p where w is the length of the arc subtending the angle (b For the preferred case of [3 45, and with k 0.8 by way of example, the foregoing inequalities yield w 1.25 p where w is the length of the arc subtending the angle 4 The differential equations leading to mathematical relationships given in connection with FIG. 4 are the same whether the elastic restoring force be supplied by the inherent resiliency of a reed or by a spiral Spring anchored to an inelastic rod. These relationships, therefore, are also applicable to the system of FIGS. 1 3 if the magnetic biasing force is replaced by that of a coiled spring fixed to pin 101 and to an extremity of bar 100.

I claim:

1. A driving mechanism for a timepiece, comprising:

a unidirectionally rotatable ratchet wheel forming part of a gear train for driving the hands of said timepiece, said ratchet wheel being provided with pointed teeth forming sloping rear flanks as viewed in the direction of rotation thereof;

electromagnetically operable stepping means engageable with said teeth for periodically advancing said ratchet wheel by increments equal to one tooth division;

an elongate pawl member engageable with said teeth at a location offset from said stepping means, said pawl member having an end face positioned to contact the rear flank of an aligned tooth between advances of said ratchet wheel and being swingable about a fulcrum lying on a line perpendicular to said rear flank in a contact position in which said end face obliquely intersects the orbit of said teeth;

and biasing means urging said pawl member into wherein contact position against the direction of advance of said ratchet teeth, said pawl member having a side face adjoining said end face and spacedly confronting the tip of an oncoming tooth immediately following said aligned tooth whereby said oncoming tooth strikes said side face during the next stepping of said ratchet wheel, .the mass of said pawl member being so related to the force of said biasing means as to cause deflection of said pawl member under the impact of said oncoming tooth to an extent and for a time suflicient to let the tip of said oncoming tooth clear said pawl member during the remainder of the stepping movement.

2. A mechanism as defined in claim 1 wherein said perpendicular line terminates substantially at the tip of said aligned tooth in said contact position.

3. A mechanism as defined in claim 1, further comprising stop means for blocking the swing pawl member past said contact position under the urging of said biasing means.

4. A mechanism as defined in claim 3 wherein said pawl member consists at least partly of ferromagnetic material, said biasing means including a magnet tending to draw said pawl member against said stop means.

5. A mechanism as defined in claim 4 wherein said magnet has two pole pieces bracketing said pawl member, said stop means being adjustably disposed between said pole pieces.

6. A mechanism as defined in claim 1 wherein said pawl member comprises an elastic reed clamped at an end remote from said ratchet wheel and provided at its opposite end with an enlarged head forming said end and side faces.

7. A mechanism as defined in claim 1 wherein said stepping means comprises a two-armed balance lever having a dog at each end alternately engageable with the teeth of said ratchet wheel.

8. A mechanism as defined in claim 7 wherein said stepping means further comprises a spiral spring anchored to said lever and a mobile electromagnetic coil mechanically connected with said spiral spring.

9. A mechanism as defined in claim 8 wherein said stepping means includes a source of periodic current pulses, said spiral spring being electrically conductive and being connected in series with said coil across said source.

10. A mechanism as defined in claim 7 45said rear flank includes an angle of substantially 45 with the radius of said ratchet wheel passing through the tip of the corresponding tooth, at least one of said dogs having a beveled face engageable with said rear flank for advancing said ratchet wheel. 

1. A driving mechanism for a timepiece, comprising: a unidirectionally rotatable ratchet wheel forming part of a gear train for driving the hands of said timepiece, said ratchet wheel being provided with pointed teeth forming sloping rear flanks as viewed in the direction of rotation thereof; electromagnetically operable stepping means engageable with said teeth for periodically advancing said ratchet wheel by increments equal to one tooth division; an elongate pawl member engageable with said teeth at a location offset frOm said stepping means, said pawl member having an end face positioned to contact the rear flank of an aligned tooth between advances of said ratchet wheel and being swingable about a fulcrum lying on a line perpendicular to said rear flank in a contact position in which said end face obliquely intersects the orbit of said teeth; and biasing means urging said pawl member into wherein contact position against the direction of advance of said ratchet teeth, said pawl member having a side face adjoining said end face and spacedly confronting the tip of an oncoming tooth immediately following said aligned tooth whereby said oncoming tooth strikes said side face during the next stepping of said ratchet wheel, the mass of said pawl member being so related to the force of said biasing means as to cause deflection of said pawl member under the impact of said oncoming tooth to an extent and for a time sufficient to let the tip of said oncoming tooth clear said pawl member during the remainder of the stepping movement.
 2. A mechanism as defined in claim 1 wherein said perpendicular line terminates substantially at the tip of said aligned tooth in said contact position.
 3. A mechanism as defined in claim 1, further comprising stop means for blocking the swing pawl member past said contact position under the urging of said biasing means.
 4. A mechanism as defined in claim 3 wherein said pawl member consists at least partly of ferromagnetic material, said biasing means including a magnet tending to draw said pawl member against said stop means.
 5. A mechanism as defined in claim 4 wherein said magnet has two pole pieces bracketing said pawl member, said stop means being adjustably disposed between said pole pieces.
 6. A mechanism as defined in claim 1 wherein said pawl member comprises an elastic reed clamped at an end remote from said ratchet wheel and provided at its opposite end with an enlarged head forming said end and side faces.
 7. A mechanism as defined in claim 1 wherein said stepping means comprises a two-armed balance lever having a dog at each end alternately engageable with the teeth of said ratchet wheel.
 8. A mechanism as defined in claim 7 wherein said stepping means further comprises a spiral spring anchored to said lever and a mobile electromagnetic coil mechanically connected with said spiral spring.
 9. A mechanism as defined in claim 8 wherein said stepping means includes a source of periodic current pulses, said spiral spring being electrically conductive and being connected in series with said coil across said source.
 10. A mechanism as defined in claim 7 45*said rear flank includes an angle of substantially 45* with the radius of said ratchet wheel passing through the tip of the corresponding tooth, at least one of said dogs having a beveled face engageable with said rear flank for advancing said ratchet wheel. 